The present invention relates to a temperature compensated accelerometer.
Accelerometer sensors are used in a variety of applications. For instance they can be used to measure the change in velocity per unit time (accelerometer applications), the pull of gravity (tilt applications) and shock and vibration. In many application areas it is required that the accelerometer have a very high degree of accuracy over a wide temperature range. For instance accelerometers used in high end inertial guidance systems typically require an accuracy of one part in 1000 over a temperature range of −40 C to +85 C. A typical tilt application of accelerometers is their use in oil well drilling systems to measure the inclination and roll angle of the drill string as the well is being drilled. This application enables the well to be directionally drilled. In this case an acceleration accuracy of one part in 1000 must be maintained over a temperature range of −30 C to +175 C.
The preferred acceleration technology used to achieve high accuracy over a wide temperature range is the Torque Balance Accelerometer (TBA). This sensor consists of an amorphous quartz hinge supporting a quartz proof mass, a support structure, a permanent magnet torquer, a capacitive pick off and self-contained analog electronics. TBA's of the prior art typically produce a non temperature compensated analog output voltage proportional to the measured acceleration.
It is well known that the temperature stability of the TBA is high due in large part to the use of amorphous quartz as the material for the system proof mass and support hinge. However for very high accuracy applications the TBA offset and scale factor must be temperature compensated. The accelerometer has an internal temperature sensor and in the prior art this compensation is performed external to the accelerometer by reading the temperature and acceleration and modeling the offset and scale factor corrections. In the prior art this correction is performed by the end user of the accelerometer after the accelerometer is installed in the user equipment.
The current invention disclosure adds integral digital processing and memory capability to the TBA. This added capability enables the digital transmission of temperature calibrated accelerometer data. This capability also enables the analog output voltage of the accelerometer to be internally temperature calibrated through the use of a high accuracy digital to analog converter.